Hollow structures and associated method for conveying refrigerant fluids

ABSTRACT

The present invention relates to the field of flexible hollow structure suitable to convey a refrigerant fluid and methods for their use. Disclosed hollow structures comprising a layer made of a resin composition comprising one or more semi-aromatic polyamides and one or more functionalized polyolefins show a balance of properties in terms of flexibility, permeation barrier against a refrigerant fluid and retention of properties upon heat and refrigerant fluid exposure.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. Provisional Application No. 61/286,977, filed Dec. 16, 2009.

FIELD OF THE INVENTION

The present invention relates to the field of flexible hollow structures that are particularly suitable for conveying refrigerant fluids.

BACKGROUND OF THE INVENTION

Hollow structures made of thermoplastic are well known for a variety of applications, like for example in the building industry for water pipes, radiator pipes or floor-heating pipes or in automotive conduits to carry many different fluids or liquid media, and are desired to display a balance of properties including thermal, mechanical and chemical resistance. In the automotive industry for example, and especially for structures made of thermoplastic materials and used to convey fluids, such structures (pipes, ducts, conduits, tubes, tubings, etc.) are desired to exhibit good mechanical properties, flexibility, impermeability and chemical resistance to the fluid(s) being conveyed. In air conditioning and refrigeration systems, the refrigerant fluid needs to be transported through and/or between various components of the system such as the compressor, condenser and evaporator.

Hollow structures used to convey refrigerant fluids are required to exhibit a balance of properties including flexibility, thermal, mechanical and chemical resistance to all of the constituents of the refrigerant fluid.

Such structures need to be flexible for ease of installation and use, and often must be shaped into curves and bends for connecting components already installed into fixed positions without kinking.

Such structures need to have a high resistance to bursting pressures and possess high impermeability to the refrigerant fluid being conveyed. It is important that the structure not suffer from deterioration leading to the loss of properties upon long term contact with the refrigerant fluid. For example, a reduction in molecular weight and concomitant loss in physical properties can result in failure of the structure during use. Such failure can be catastrophic, with the loss of refrigerant fluid causing the impairment of the performance of the device within which the hollow structure is incorporated.

Due to the difficulty of meeting all these needs with a single material, multilayer hollow structures have been developed. The layers of such structures often comprise dissimilar materials to satisfy specified performance criteria by placing different materials at the most appropriate position in the structure. The multilayer hollow structure may comprise one or more barrier layers made of a thermoplastic resin that possess high impermeability to the refrigerant fluid, one or more elastomeric layers to provide flexibility, one or more layers of braiding to provide burst strength to withstand the refrigerant fluid pressure, and adhesive layers disposed between any of these layers to provide adhesion.

Polyamides are a desirable material to use for hoses and pipes because they have good chemical resistance, good physical properties, and can be conveniently formed into hoses with a variety of diameters and incorporated into multilayered hoses. Certain short chain polyamides and copolyamides, especially PA 6, PA 66 and PA 66/6 possess good impermeability to refrigerant fluids, and are thus commonly used to form thermoplastic resin barrier layers of the hollow structure used to convey refrigerant fluids. These polyamides may further comprise plasticizers and/or toughening agents.

European Pat. No. 0,945,660 discloses a multilayer hose comprising an innermost layer comprising a polyamide, especially polyamide 6, and optionally a polyolefin rubber, an intermediate reinforcing layer made of aramid fibers and an outermost layer made of an ethylene acrylic rubber.

Unfortunately, the existing technologies that are used to prepare hollow structures for conveying refrigerant fluids suffer from deterioration of their mechanical properties upon high temperature exposure in the presence of a refrigerant fluid.

A need remains for hollow structures used for conveying refrigerant fluids that have a good balance of properties in terms of flexibility, impermeability to the refrigerant fluid being conveyed and a good retention of mechanical and structural properties upon exposure to heat in the presence of a refrigerant fluid.

SUMMARY OF THE INVENTION

There is disclosed a use of a hollow structure for conveying a refrigerant fluid, said hollow structure comprising a layer made of a resin composition comprising one or more semi-aromatic polyamides and one or more functionalized polyolefins,

wherein the one or more semi-aromatic polyamides are selected from copolyamides made from: a) group A monomers selected from:

-   -   i) aromatic dicarboxylic acids having 8 to 20 carbon atoms and         aliphatic diamines having 4 to 20 carbon atoms; or     -   ii) aliphatic dicarboxylic acids having 6 to 20 carbon atoms and         aromatic diamine having 6 to 20 carbon atoms; or     -   iii) aromatic aminocarboxylic acids having 7 to 20 carbon atoms;         and         b) group B monomers selected from:     -   iv) aliphatic dicarboxylic acids having 6 to 20 carbon atoms and         aliphatic diamines having 4 to 20 carbon atoms; or     -   v) lactams and/or aliphatic aminocarboxylic acids having 4 to 20         carbon atoms,         wherein the monomers of group A are present in an amount from at         or about 10 mole-percent to at or about 40 mole-percent based on         the copolyamide, and the monomers of group B are present in an         amount from at or about 60 mole-percent to at or about 90         mole-percent based on the copolyamide.

Further described herein is a refrigerant device comprising the hollow structure described above.

Further described herein is method for conveying a refrigerant fluid comprising a step of passing the refrigerant fluid through the hollow structure described above.

DETAILED DESCRIPTION OF THE INVENTION

As used throughout the specification, the phrases “about” and “at or about” are intended to mean that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. In general, an amount, size, formulation, parameter or other quantity or characteristic is “about” or “approximate” whether or not expressly stated to be such.

The term “fluid” refers to a substance that flows and conforms to the outline of its container, a fluid can be a liquid or a gas.

The terms “pipe”, “duct”, “conduit”, “tube” and “tubing” are used interchangeably herein to denote a hollow structure, i.e. any structure having an empty or concave interior part used to convey a fluid.

The hollow structure according to the present invention comprises a layer made of a resin composition comprising one or more semi-aromatic polyamides and one or more functionalized polyolefins.

The one or more semi-aromatic polyamides comprised in the resin composition described herein are selected from copolyamides made from:

a) group A monomers selected from:

-   -   i) aromatic dicarboxylic acids having 8 to 20 carbon atoms and         aliphatic diamines having 4 to 20 carbon atoms; or     -   ii) aliphatic dicarboxylic acids having 6 to 20 carbon atoms and         aromatic diamine having 6 to 20 carbon atoms; or     -   iii) aromatic aminocarboxylic acids having 7 to 20 carbon atoms;         and         b) group B monomers selected from:     -   iv) aliphatic dicarboxylic acids having 6 to 20 carbon atoms and         aliphatic diamines having 4 to 20 carbon atoms; or     -   v) lactams and/or aliphatic aminocarboxylic acids having 4 to 20         carbon atoms,         wherein the monomers of group A are present in an amount from at         or about 10 mole-percent to at or about 40 mole-percent,         preferably from at or about 15 mole-percent to at or about 35         mole-percent, based on the copolyamide, and the monomers of         group B are present in an amount from at or about 60         mole-percent to at or about 90 mole-percent, preferably from at         or about 65 mole-percent to at or about 85 mole-percent based on         the copolyamide.

Suitable aromatic dicarboxylic acids having 8 to 20 carbon atoms include terephthalic acid, isophthalic acid, phthalic acid, 2-methyl terephthalic acid, diphenic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic, 1,5-nathphalenedicarboxylic acid; 2,6-nathphalenedicarboxylic acid; terephthalic acid and isophthalic acid being preferred.

Suitable aliphatic dicarboxylic acids having 6 to 20 carbon atoms include adipic acid (C6), pimelic acid (C7), suberic acid (C8), azelaic acid (C9), decanedioic acid (C10), undecanedioic acid (C11), dodecanedioic acid (C12), tridecanedioic acid (C13), tetradecanedioic acid (C14), and pentadecanedioic acid (C15), hexadecanoic acid (C16), octadecanoic acid (C18) and eicosanoic acid (C20).

Suitable aliphatic diamines having 4 to 20 carbon atoms include tetramethylene diamine, hexamethylene diamine, octamethylene diamine, nonamethylenediamine, decamethylene diamine, dodecamethylene diamine, 2-methylpentamethylene diamine, 2-ethyltetramethylene diamine, 2-methyloctamethylene diamine, trimethylhexamethylene diamine, and bis(p-aminocyclohexyl)methane.

Suitable aromatic diamines having 6 to 20 carbon atoms include m-xylylenediamine and p-xylylenediamine.

Suitable aromatic aminocarboxylic acids having 7 to 20 carbon atoms include p-aminobenzoic acid, m-aminobenzoic acid, anthranilic acid 6-amino-2-naphthoic acid.

Suitable lactams include caprolactam and laurolactam.

A suitable aliphatic aminocarboxylic acid includes 11-aminoundecanoic acid.

Preferably, the one or more semi-aromatic polyamides comprised in the resin composition described herein are selected from copolyamides made from:

a) group A monomers selected from:

-   -   i) aromatic dicarboxylic acids selected from terephthalic acid,         isophthalic acid and mixtures thereof and aliphatic diamines         having 4 to 10 carbon atoms; or     -   ii) aliphatic dicarboxylic acids having 6 to 14 carbon atoms and         aromatic diamine having 6 to 10 carbon atoms; or     -   iii) aromatic aminocarboxylic acids having 7 to 10 carbon atoms         and         b) group B monomers selected from:     -   iv) aliphatic dicarboxylic acids having 6 to 10 carbon atoms and         aliphatic diamines having 4 to 10 carbon atoms; or     -   v) lactams and/or aliphatic aminocarboxylic acids having 4 to 12         carbon atoms.

More preferably, the one or more semi-aromatic polyamides are selected from copolyamides made from:

a) group A monomers selected from terephthalic acid and hexamethylenediamine or terephthalic acid and tetramethylenediamine; and b) group B monomers selected from adipic acid and tetramethylenediamine; adipic acid and hexamethylenediamine; decanedioic acid and hexamethylenediamine; dodecanedioic acid and hexamethylenediamine; caprolactam; laurolactam; 11-aminoundecanoic acid;

a) group A monomers selected terephthalic acid and decamethylenediamine; and b) group B monomers selected from decanedioic acid and decamethylenediamine;

a) group A monomers selected adipic acid and m-xylylenediamine; and b) group B monomers selected from adipic acid and hexamethylenediamine;

and mixtures thereof.

Still more preferably, the one or more semi-aromatic polyamides are selected from copolyamides made from: a) group A monomers selected from terephthalic acid and hexamethylenediamine and b) group B monomers selected from adipic acid and hexamethylenediamine.

The copolyamides described herein may be prepared by any means known to those skilled in the art, such as in a batch process using, for example, an autoclave or using a continuous process. See, for example, Kohan, M. I. Ed. Nylon Plastics Handbook, Hanser: Munich, 1995; pp. 13-32. Generally, the monomers are allowed to react to form a random chain of interlinked monomers.

The resin composition described herein comprises one or more functionalized polyolefins. The one or more functionalized polyolefins may be used alone or may be used in combination with the one or more unfunctionalized polyolefins described below. The term “functionalized polyolefin” refers to an alkylcarboxyl-substituted polyolefin, which is a polyolefin that has carboxylic moieties attached thereto, either on the polyolefin backbone itself or on side chains. The term “carboxylic moiety” refers to carboxylic groups, such as carboxylic acids, carboxylic acid ester, carboxylic acid anhydrides and carboxylic acid salts.

Functionalized polyolefins may be prepared by direct synthesis or by grafting. An example of direct synthesis is the polymerization of ethylene and/or at least one alpha-olefin with at least one ethylenically unsaturated monomer having a carboxylic moiety. An example of grafting process is the addition of at least one ethylenically unsaturated monomer having at least one carboxylic moiety to a polyolefin backbone. The ethylenically unsaturated monomers having at least one carboxylic moiety may be, for example, mono-, di-, or polycarboxylic acids and/or their derivatives, including esters, anhydrides, salts, amides, imides, and the like. Suitable ethylenically unsaturated monomers include methacrylic acid; acrylic acid; ethacrylic acid; glycidyl methacrylate; 2-hydroxy ethylacrylate; 2-hydroxy ethyl methacrylate; diethyl maleate; monoethyl maleate; di-n-butyl maleate; maleic anhydride; maleic acid; fumaric acid; mono- and disodium maleate; acrylamide; glycidyl methacrylate; dimethyl fumarate; crotonic acid, itaconic acid, itaconic anhydride; tetrahydrophthalic anhydride; monoesters of these dicarboxylic acids; dodecenyl succinic anhydride; 5-norbornene-2,3-anhydride; nadic anhydride (3,6-endomethylene-1,2,3,6-tetrahydrophthalic anhydride); nadic methyl anhydride; and the like. Since polyolefins are incompatible with polyamides, it is necessary to modify them with functional groups that are capable of reacting with the acid or amine ends of the polyamide polymer. Due to the fact that the reaction of an anhydride with an amine is very fast, anhydrides are preferred grafting agents and more preferably maleic anhydride is chosen.

Preferably, the one or more functionalized polyolefins are one or more grafted polyolefins. The grafting agents, i.e. the at least one monomer having at least one carboxylic moiety, is preferably present in the one or more functionalized polyolefins in an amount from at or about 0.05 to at or about 6 weight percent, preferably from at or about 0.1 to at or about 2.0 weight percent, the weight percentages being based of the total weight of the one or more functionalized polyolefins.

Grafted polyolefins are preferably derived by grafting at least one monomer having at least one carboxylic moiety to a polyolefin, an ethylene alpha-olefin or a copolymer derived from at least one alpha-olefin and a diene. Preferably, the resin composition described herein comprises grafted polyolefins selected from grafted polyethylenes, grafted polypropylenes, grafted ethylene alpha-olefin copolymers, grafted copolymers derived from at least one alpha-olefin and a diene and mixtures thereof. More preferably, the resin composition described herein comprises maleic anhydride grafted polyolefins selected from maleic anhydride grafted polyethylenes, maleic anhydride grafted polypropylenes, maleic anhydride grafted ethylene alpha-olefin copolymers, maleic anhydride grafted copolymers derived from at least one alpha-olefin and a diene and mixtures thereof.

Polyethylenes used for preparing maleic anhydride grafted polyethylene (MAH-g-PE) are commonly available polyethylene resins selected from HDPE (density higher than 0.94 g/cm³), LLDPE (density of 0.915-0.925 g/cm³) or LDPE (density of 0.91-0.94 g/cm³). Polypropylenes used for preparing maleic anhydride grafted polypropylene (MAH-g-PP) are commonly available copolymer or homopolymer polypropylene resins.

Ethylene alpha-olefins copolymers comprise ethylene and one or more alpha-olefins, preferably the one or more alpha-olefins have 3-12 carbon atoms. Examples of alpha-olefins include but are not limited to propylene, 1-butene, 1-pentene, 1-hexene-1,4-methyl 1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene and 1-dodecene. Preferably the ethylene alpha-olefin copolymer comprises from at or about 20 to at or about 96 weight percent of ethylene and more preferably from at or about 25 to at or about 85 weight percent; and from at or about 4 to at or about 80 weight percent of the one or more alpha-olefins and more preferably from at or about 15 to at or about 75 weight percent, the weight percentages being based on the total weight of the ethylene alpha-olefins copolymers. Preferred ethylene alpha-olefins copolymers are ethylene-propylene copolymers and ethylene-octene copolymers.

Copolymers derived from at least one alpha-olefin and a diene are preferably derived from alpha-olefins having preferably 3-8 carbon atoms. Preferred copolymers derived from at least one alpha-olefin and a diene are ethylene propylene diene elastomers. The term “ethylene propylene diene elastomers (EPDM)” refers to any elastomer that is a terpolymer of ethylene, at least one alpha-olefin, and a copolymerizable non-conjugated diene such as norbornadiene, 5-ethylidene-2-norbornene, dicyclopentadiene, 1,4-hexadiene and the like. When a functionalized ethylene propylene diene elastomer is comprised in the resin composition described herein, the ethylene propylene diene polymer preferably comprise from at or about 50 to at or about 80 weight percent of ethylene, from at or about 10 to at or about 50 weight percent of propylene and from at or about 0.5 to at or about 10 weight percent of at least one diene, the weight percentages being based on the total weight of the ethylene propylene diene elastomer.

The one or more functionalized polyolefins are preferably present in the resin composition described herein in an amount from at or about 5 to at or 40 weight percent and more preferably from at or about 10 to at or 30 weight percent, the weight percentages being based on the total weight of the resin composition.

The resin composition described herein may further comprise one or more unfunctionalized polyolefins. Preferably, the one or more unfunctionalized polyolefins are selected from unfunctionalized polyethylenes, unfunctionalized polypropylenes, unfunctionalized ethylene alpha-olefin copolymers such as those described above, unfunctionalized ethylene propylene diene rubbers (EPDM) such as those described above and mixtures thereof. When present, the one or more unfunctionalized polyolefins are preferably present in the resin composition described herein in an amount from at or about 5 to at or 40 weight percent and more preferably from at or about 10 to at or 30 weight percent, the weight percentages being based on the total weight of the resin composition.

The resin composition described herein may further comprise one or more ionomers. Ionomers are thermoplastic resins that contain metal ions in addition to the organic backbone of the polymer such as for example copolymers of an olefin such as ethylene with partially neutralized (from 10 to 99.9%) alpha, beta-unsaturated C₃-C₈ carboxylic acid. Preferred alpha, beta-unsaturated C₃-C₈ carboxylic acids are acrylic acid (AA), methacrylic acid (MAA) or maleic acid monoethylester (MAME). Neutralizing agents are alkali metals like lithium, sodium or potassium or transition metals like manganese or zinc. When present, the one or more ionomers are preferably present in the resin composition described herein in an amount from at or about 5 to at or 40 weight percent and more preferably from at or about 10 to at or 30 weight percent, the weight percentages being based on the total weight of the resin composition. Suitable ionomers for use in the present invention are commercially available under the trademark Surlyn® from E. I. du Pont de Nemours and Company, Wilmington, Del.

The resin composition described herein may further comprise one or more plasticizers. Preferably, the one or more plasticizers are selected from sulfonamides, esters of hydroxybenzoic acids, tetrahydrofurfuryl alcohol esters or ethers, esters of citric acid or of hydroxymalonic acid and mixtures thereof. Examples of plasticizer include without limitation sulfonamides, esters of hydroxybenzoic acids, such as ethyl p-hydroxybenzoate, 2-ethylhexyl para-hydroxybenzoate, octyl p-hydroxybenzoate, 2-decylhexyl para-hydroxybenzoate or isohexadecyl p-hydroxybenzoate; tetrahydrofurfuryl alcohol esters or ethers, such as oligoethoxylated tetrahydrofurfuryl alcohol; esters of citric acid or of hydroxymalonic acid, such as oligoethoxylated malonate. Mention may also be made of decylhexyl para-hydroxybenzoate and ethylhexyl para-hydroxybenzoate. Preferably, the one or more plasticizers are sulphonamides and more preferably aromatic sulfonamides such as benzenesulfonamides and toluenesulfonamides. Examples of suitable aromatic sulfonamides include N-alkyl benzenesulfonamides and toluenesulfonamides, such as N-butylbenzenesulfonamide (BBSA), N-(2-hydroxypropyl)benzenesulfonamide, N-cyclohexyltoluenesulphonamide; N-n-octyltoluenesulfonamide, N-2-ethylhexylbenzenesulfonamide, N-ethyl-o-toluenesulfonamide, N-ethyl-p-toluenesulfonamide, o-toluenesulfonamide, p-toluenesulfonamide, and the like. Preferred aromatic sulfonamides are N-butylbenzenesulfonamide, N-ethyl-o-toluenesulfonamide, and N-ethyl-p-toluenesulfonamide, are N-butylbenzenesulfonamide being particularly preferred. When present, the one or more plasticizers are preferably present in the resin composition described herein in an amount from at or about 1 to at or 20 weight percent and more preferably from at or about 5 to at or 15 weight percent, the weight percentages being based on the total weight of the resin composition. The plasticizer may be incorporated into the resin composition by melt-blending the polymer with plasticizer and, optionally, other ingredients, or during polymerization. If the plasticizer is incorporated during polymerization, the polyamide monomers are blended with one or more plasticizers prior to starting the polymerization cycle and the blend is introduced to the polymerization reactor. Alternatively, the plasticizer can be added to the reactor during the polymerization cycle.

The resin composition described herein may further comprise one or more heat stabilizers. Preferably, the one or more heat stabilizers are selected from copper salts and/or copper salt derivatives such as for example copper halides or copper acetates; divalent manganese salts and/or derivatives thereof and mixtures thereof. Preferably, copper salts are used in combination with halide compounds and/or phosphorus compounds and more preferably copper salts are used in combination with iodide or bromide compounds, and still more preferably, with potassium iodide or potassium bromide. When present, the one or more heat stabilizers are preferably present in the resin composition described herein in an amount from at about 0.1 to about 3 weight percent and preferably from at or about 0.1 to at or about 1 weight percent, the weight percentages being based on the total weight of the resin composition.

The resin composition described herein may further comprise one or more antioxidants such as phosphorus stabilizers (e.g. phosphate or phosphonite stabilizers), hindered phenol stabilizers, hindered amine stabilizers, aromatic amine stabilizers, thioesters, and phenolic based anti-oxidants that hinder thermally induced oxidation of polymers where high temperature applications are used. Preferably, the one or more antioxidants are selected from hindered phenol stabilizers, hindered amine stabilizers, phosphorus antioxidants and mixtures thereof. When present, the one or more antioxidants are preferably present in the resin composition described herein in an amount from at or about 0.1 to at or about 3 weight percent and preferably from at or about 0.1 to at or about 1 weight percent, the weight percentages being based on the total weight of the resin composition.

The resin composition described herein may further comprise modifiers and other ingredients, including, without limitation, lubricants and mold release agents (including stearic acid, stearyl alcohol and stearamides, and the like), flame retardants, antistatic agents, coloring agents (including dyes, pigments, carbon black, and the like), nucleating agents and other processing aids known in the polymer compounding art.

The resin composition described herein may further comprise fillers and reinforcing agents such as mineral fillers, glass fibers, nano particulates, carbon fibers, metal fibers and metal-coated fibers.

The resin compositions described herein are preferably melt-mixed blends, wherein all of the polymeric components are well-dispersed within each other and all of the non-polymeric ingredients are well-dispersed in and bound by the polymer matrix, such that the blend forms a unified whole. Any melt-mixing method may be used to combine the polymeric components and non-polymeric ingredients of the present invention. For example, the polymeric components and non-polymeric ingredients may be added to a melt mixer, such as, for example, a single or twin-screw extruder; a blender; a single or twin-screw kneader; or a Banbury mixer, either all at once through a single step addition, or in a stepwise fashion, and then melt-mixed. When adding the polymeric components and non-polymeric ingredients in a stepwise fashion, part of the polymeric components and/or non-polymeric ingredients are first added and melt-mixed with the remaining polymeric components and non-polymeric ingredients being subsequently added and further melt-mixed until a well-mixed composition is obtained.

The hollow structures described herein exhibit a good retention of mechanical properties upon exposure to a refrigerant fluid and are therefore particularly suitable in applications where the layer made of the resin composition described herein is in contact with a refrigerant fluid. The hollow structure is preferably in the form of a hose, a pipe, a duct, a tube, tubing or a conduit. Due to the advantages mentioned above, the hollow structures described herein are particularly suitable for use in applications that require conveying a refrigerant fluid or a refrigerant-containing composition. Preferably, the refrigerant fluid that is conveyed by the hollow structure described herein comprises a hydrofluoroolefin (HFO) and more preferably 2,3,3,3-tetrafluoropropene. Refrigerants fluids comprising fluorocarbon compounds based on hydrofluoroolefins (HFOs) and especially tetrafluoropropenes (such as for example HFO-1234) are particularly suitable. Hydrofluoroolefins (HFOs) are unsaturated compounds, preferably having at least one double bond, comprising at least one fluorine atom substituent and at least one hydrogen atom. Refrigerant-containing compositions may comprise a variety of optional additives including lubricants (e.g. mineral oil, polyalkylene glycol, polyalkylene glycol ester, polyvinyl ethers, and polyol esters), stabilizers (e.g. dienes, phosphates, phenols and epoxides), metal passivators, corrosion inhibitors, flammability suppressants, and the like.

While for many applications the hollow structure described herein can be circular in cross-section, other shapes including elliptical or other non-circular shapes are also contemplated. The walls of the hollow structure described herein may be smooth or may comprise corrugated regions that are interrupted by smooth regions (hereafter called “partially corrugated hoses”) or can be corrugated all along its length (hereafter called “continuously corrugated hoses”). Continuously or partially corrugated hollow structures described herein enable complex routing of the pipes in constrained spaces, such as those available in underhood areas of automobiles and other vehicles.

The hollow structure described herein may be manufactured by any melt extrusion process including blow molding, profile extrusion and corrugated extrusion. Profile extrusion and corrugated extrusion are conventional techniques used for manufacturing hollow plastic bodies in arbitrary long lengths. During profile and corrugated extrusion, the composition is extruded in a hot moldable state through the gap between the pin and the die of an extrusion head. By “profile extrusion”, it is meant a technique used to produce a hollow article having the same cross section over a long length. The pin and die are shaped to produce the desired cross-section, and for example an annular die-gap between concentric circular pin and die is used to make tubes and pipes. After it exits the die assembly, the melt may be drawn to a thinner cross section through an air gap. The melt is then cooled and its shape is maintained. By “corrugated extrusion”, it is meant a technique used to produce hollow articles comprising corrugated regions that may be interrupted by smooth regions. In this case, the pin and the die are positioned inside the two halves of the mold blocks of the equipment. When the molten material coming from the extrusion head reaches the mold blocks, it is drawn up to the shape of the mold article either by heated air or by vacuum expansion against the surface of the mold cavity. Such process is described for example in U.S. Pat. Nos. 6,764,627 and 4,319,872 and Intl. Pat. App. Pub. No. WO 03/055664.

Also described herein are multilayer hollow structures comprising a layer made of the resin composition described above and one or more additional layers. In multilayer hollow structures, the layer made of the resin composition described herein may be used as a barrier layer in the hollow structure or as a veneer layer. The term “barrier layer” refers to a layer that is not in direct contact with the refrigerant fluid. The term “veneer layer” refers to a layer that is in direct contact with the refrigerant fluid. A so-called veneer structure comprises the resin composition described herein as its innermost layer in direct contact with the refrigerant fluid. Fittings may inserted into the end of the hollow structure. If the hollow structure has a hard surface, specially designed fittings often comprising O-rings can be used to provide leak-proof sealing between the surface of the fitting and the resin composition described herein.

A so-called barrier structure comprises a resin made of a material other than the resin composition described herein, such as for example an elastomeric material, as its innermost layer, in direct contact with the refrigerant fluid and a barrier layer made of the resin composition described herein located outward of the innermost layer. Given that elastomeric materials are flexible, it is often able to provide sealing against the surface of a fitting inserted into the end of the hollow structure. In this latter structure, the barrier layer made of the resin composition described herein is sandwiched between at least two other layers of the multilayer structure.

Examples of multilayer hollow structure include without limitation multilayer hollow structures comprising one or more barrier layers made of the resin composition described herein and an innermost layer made of a material other than the resin composition described herein; multilayer hollow structures comprising one or more layers made of the resin composition described herein and an outermost layer made of a material other than the resin composition described herein; multilayer hollow structures comprising one or more layers made of the resin composition described herein, an innermost layer and an outermost layer made of a material other than the resin composition described herein; and multilayer hollow structures comprising one or more layers made of the resin composition described herein and one or more functional layers; and combinations thereof.

Described herein are multilayer hollow structures comprising one or more layers made of the resin composition described herein and an innermost layer made of a material other than the resin composition described herein. The term “innermost layer” refers to a layer that is in direct contact with the refrigerant fluid to be conveyed. Preferably, the innermost layer comprises an elastomeric material that is able to seal against the surface of a fitting inserted at one of the ends of the structure. The elastomeric material is preferably a non-fluorinated rubber. Preferred non-fluorinated rubbers are selected from acrylonitrile-butadiene rubber (NBR), hydrogenated acrylonitrile-butadiene rubber (HNBR), epichlorohydrin rubber (ECO), chlorosulfonated rubber (CSM), butyl rubber (IIR) and mixtures thereof. Alternately, the innermost layer can comprise of a thermoplastic material selected from polyamides, polyesters and TEE.

Also described herein are multilayer hollow structures comprising one or more layers made of the resin composition described herein and an outermost layer made of a material other than the resin composition described herein. The term outermost layer refers to a layer that faces the environment. In general, the outermost layer may be made of one or more suitable elastomeric or plastic materials designed to withstand the exterior environment encountered. The material for the outermost layer is not specifically limited, but examples thereof include polyamide resins, polyolefin resins and thermoplastic elastomers and rubbers, which may be used either alone or in combination. Examples of thermoplastic elastomers and rubbers include without limitation acrylonitrile-butadiene rubber (NBR), hydrogenated acrylonitrile-butadiene rubber (HNBR), butyl rubber (IIR), chlorosulfonated polyethylene (CSM), polychloroprene rubber (CR), epichlorohydrin rubber (ECO), ethylene-vinyl acetate (EVM), ethylene methylacrylate elastomer (EAM), acrylic or acrylate elastomer (ACM), nitrile-polyvinylchloride (NBR-PVC) blended elastomer, chlorinated polyethylene (CPE), ethylene-alpha-olefin elastomer, ethylene-propylene-diene elastomer (EPDM) and mixtures thereof.

The multilayer hollow structures described herein may further comprise one or more functional layers, which functional layers may be situated over the outermost layer or inside the innermost layer of the hollow structure. The one or more functional layers include but are not limited to braidings, reinforcement layers, thermal shields and softer cover layers. Examples of braidings may be filament braidings with polyamide, aramid, polyethylene terephthalate (PET) or metallic filaments and woven fabrics of these materials. Examples of thermal shields may be metallic foils such as aluminum foils. Examples of softer cover layers may be layers made of rubber or of a thermoplastic elastomer.

Should the adhesion between the layer made of the resin composition described herein and the one or more additional layers be insufficient, one or more adhesive layers (also called tie layers, intervening tie layers or adhesion-promoting layers) may be added between the different layers.

The multilayer hollow structures described herein can be manufactured by conventional processes like for example extrusion, blow molding, injection molding, and corrugated extrusion. When the layer made of the resin composition described herein is adjacent to and directly in contact with a layer made of a second thermoplastic material, these layers may be manufactured by processes such as coextrusion or coextrusion blowmolding. Examples of a second thermoplastic material include materials comprising for example a polyamide, a copolyamide, a polyester, a polyesterether, a functionalized polyolefin or a thermoplastic vulcanizate. In a multilayer co-extrusion process, separate extruders are used to extrude each type of polymeric compositions. The temperature settings and other processing conditions for the extruders are arranged such that they are appropriate to the composition being extruded. This avoids having to expose lower melting polymeric compositions to higher than normal processing temperatures during the extrusion step while allowing the extrusion of higher melting polymeric compositions at a suitable temperature. The individual melts from the extrusion streams are combined together in a suitably designed die and arranged in the desired multilayer arrangement

The multilayer hollow structure comprising at least one layer made of the resin composition described herein and layers made of elastomeric materials can be made by a sequential process wherein each individual layer is extruded in sequence over a pre-extruded underlying layer, braiding layer is constructed at appropriate location, and the complete hollow structure is cured in order to cure the elastomeric layers. For example, in order to construct a veneer structure with circular cross-section, one barrier layer, one braiding layer and two elastomeric layers may be constructed as follows: a hollow structure made of the resin composition described herein is first extruded to form the innermost layer and a layer of uncured elastomeric compound is then extruded over the first layer to form a second layer of the hose. The elastomeric compound may be modified to enhance its adhesion to the layer made of the resin composition described herein. Given the high softness of the uncured elastomeric compound layer at room temperature, the structure may be cooled to a low temperature, and then a braiding layer of filaments may be applied over the elastomeric layer. A second layer of the same or a different uncured elastomeric compound is then extruded over the braiding layer. Finally the entire structure is subjected to a curing process to cure the elastomeric layers and ensure adhesion among the respective layers to form the multilayer hollow structure comprising a layer made of the resin composition described herein.

In another aspect, the present invention relates to a method for conveying a refrigerant fluid comprising a step of passing the refrigerant fluid through the hollow structure described herein.

In another aspect, the present invention relates a refrigerant device comprising the hollow structure described herein. Examples of refrigerant device include without limitation automotive air-conditioning systems, building heating, ventilation and air conditioning systems, refrigerated storage systems, refrigerated transportation systems and such where a refrigerant fluid needs to be conveyed between various components of the device.

EXAMPLES

The Examples below provide greater detail for the compositions, uses and processes described herein.

The following materials were used for preparing the resin composition to be used to make the hollow structure of the present invention and a comparative example.

Materials

Polyamide PA66/6T: copolyamide made from a) group A monomers consisting of terephthalic acid and hexamethylenediamine; and b) group B monomers consisting of adipic acid and hexamethylenediamine, wherein the monomers of group A are present in an amount of 25 mole-percent and the monomers of group B are present in an amount of 75 mole-percent, the weight percentages being based on the copolyamide. Polyamide PA6 Compound: a commercially available PA6 described as an extrudable super tough polyamide 6 resin suitable for hose inner cores, such a product is commercially available from E. I. du Pont de Nemours and Company, Wilmington, Del. under the tradename Zytel® ST811 HS NC 010. MAH-g-ethylene octene copolymer: ethylene octene copolymer comprising 72 weight percent of ethylene, 28 weight percent of octene and about 0.6 weight percent of grafted maleic anhydride. Ethylene-octene polymer: a polymer comprising 72 weight percent of ethylene, 28 weight percent of octene supplied from Dow Chemicals under the name Engage™. N-butyl benzene sulphonamide: plasticizer supplied by Unitex Chemical Corportation, Greensboro, N.C., USA under the name Uniplex 214

Antioxidant 1: N,N′-hexane-1,6-diylbis(3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide)) supplied by Ciba Specialty Chemicals, Tarrytown, N.Y., USA under the tradename Irganox® 1098.

Antioxidant 2: tris(2,4-ditert-butylphenyl)phosphite supplied by Ciba Specialty Chemicals, Tarrytown, N.Y., USA under the tradename Irgafox® 168. Heat stabilizer: mixture of potassium iodide, copper iodide and aluminum distearate in a 7:1:1 ratio. Refrigerant fluid: a mixture comprising 50% of HFO 1234 yf (2,3,3,3-tetrafluoropropene supplied by DuPont, 50% of a proprietary polyalkylene glycol (PAG) based lubricant referred to as ND8S5 supplied by Idemitsu and 2000 ppm H₂O based on the weight of the oil.

Compounding. The composition of the Example (E1) was prepared by melt blending ingredients shown in Table 1 in a ZSK 25 mm twin screw extruder operating at about 260° C. and a throughput of about 15 kg/h. Ingredient quantities shown in Table 1 are given in weight percent on the basis of the total weight of the resin composition. The compounded mixture was extruded in the form of laces or strands, cooled in a water bath, chopped into granules and placed into sealed aluminum lined bags in order to prevent moisture pick up. The composition of the Comparative Example (C1) was used as commercially available resin form. All materials were dried overnight at 70° C. in a dehumidified drier prior to further use.

Preparation of test pieces. The compositions E1 and C1 were extruded into a thin sheet. E1 composition was extruded into a 0.17 mm thick flat sheet using a sheet casting line with 45 mm (1.75″) 24:1 L/D Wayne extruder with a 200 mm (8″) wide coathanger type sheet die at a melt temperature of about 260° C. Dogbone shaped tensile test pieces measuring 63 mm long, 3.2 mm wide in the gauge section and 9.5 mm wide at the ends were die-cut from the sheet. Dogbone shaped tensile test pieces from a 0.15 mm thick sheet of composition C1 were procured for comparative testing. These test pieces measured about 45 mm long, 6 mm wide in the gauge section and 17 mm wide at the ends.

Heat ageing in the presence of a refrigerant fluid. The test specimens were dried at 60° C. for 24 hrs in a dehumidified dryer, and individually sealed into glass tubes containing 4 mL of the refrigerant fluid (as described in the “Materials” section). Two tubes were prepared for test pieces of composition E1 and three tubes were prepared for test pieces of composition C1. The tubes were heated in an oven with circulating hot air at a temperature of 150° C. for 300 hours. At the end of the heating, the glass tubes were broken and the test pieces were retrieved for measurements.

Measurements

Tensile properties of the test pieces before and after heat ageing were measured at room temperature on a tensile tester by gripping the wide ends of the dogbone shaped test pieces in the upper and lower grips, and stretching the test pieces at a crosshead speed of 50 mm/min. The average values of tensile strength before and after heat ageing are given in Table 1.

Following tensile measurements, broken test pieces were retained and used for the determination of weight average molecular weight (MW) by SEC method using THF solvent and refractive index detector.

Polyamide or copolyamide phase of each composition was thus dissolved and the solution was used to determine the MW. The average values of MW before and after heat ageing are given in Table 1.

The retention of tensile strength and MW is reported as the percentage of the tensile strength and MW retained after aging at 150° C. for 300 hours, in comparison with the value of the specimens prior to ageing (i.e. unaged) considered as being 100%. Retention results are given in Table 1.

TABLE 1 C1 E1 compositions PA6 100 — PA66/6T — 68.7 MAH-g-ethylene octene copolymer — 15 ethylene-octene polymer — 15 antioxidant 1 — 0.5 antioxidant 2 — 0.5 heat stabilizer — 0.3 Tensile Unaged 35 13 Strength/ After ageing at 150° C. for 300 hours 20 13 MPa Retention 58% 100% Average Unaged 53459 28431 Mw After ageing at 150° C. for 300 hours 32138 21030 Retention 60% 74%

As shown in Table 1, test pieces made of the composition E1 comprising a semi-aromatic copolyamide and a functionalized polyolefin exhibited improved retention of the tensile strength and MW at the end of ageing test compared to comparative test pieces mad of composition C1. 

1. A use of a hollow structure for conveying a refrigerant fluid, said hollow structure comprising a layer made of a resin composition comprising one or more semi-aromatic polyamides and one or more functionalized polyolefins, wherein the one or more semi-aromatic polyamides are selected from copolyamides made from: a) group A monomers selected from: i) aromatic dicarboxylic acids having 8 to 20 carbon atoms and aliphatic diamines having 4 to 20 carbon atoms; or ii) aliphatic dicarboxylic acids having 6 to 20 carbon atoms and aromatic diamine having 6 to 20 carbon atoms; or iii) aromatic aminocarboxylic acids having 7 to 20 carbon atoms and b) group B monomers selected from: iv) aliphatic dicarboxylic acids having 6 to 20 carbon atoms and aliphatic diamines having 4 to 20 carbon atoms; or v) lactams and/or aliphatic aminocarboxylic acids having 4 to 20 carbon atoms, wherein the monomers of group A are present in an amount from at or about 10 mole-percent to at or about 40 mole-percent based on the copolyamide, and the monomers of group B are present in an amount from at or about 60 mole-percent to at or about 90 mole-percent based on the copolyamide.
 2. The use according to claim 1, wherein the one or more functionalized polyolefins are maleic anhydride grafted polyolefins.
 3. The use to claim 1 or 2, wherein the one or more functionalized polyolefins are selected from maleic anhydride grafted polyethylenes, maleic anhydride grafted polypropylenes, maleic anhydride grafted ethylene alpha-olefin copolymers or maleic anhydride grafted ethylene-propylene diene rubber and mixtures thereof.
 4. The use according to claim 2 or 3, wherein the one or functionalized polyolefins are present in an amount from 10 to 30 weight percent, the weight percentages being based on the total weight of the composition.
 5. The use according to any preceding claim, wherein the one or more semi-aromatic polyamides are selected from copolyamides made from: a) group A monomers selected from terephthalic acid and hexamethylenediamine; terephthalic acid and tetramethylenediamine; and b) group B monomers selected from adipic acid and tetramethylenediamine; adipic acid and hexamethylenediamine; decanedioic acid and hexamethylenediamine; dodecanedioic acid and hexamethylenediamine; caprolactam; laurolactam; 11-aminoundecanoic acid; a) group A monomers selected terephthalic acid and decamethylenediamine; and b) group B monomers selected from decanedioic acid and decamethylenediamine; a) group A monomers selected adipic acid and m-xylylenediamine; and b) group B monomers selected from adipic acid and hexamethylenediamine; and mixtures thereof.
 6. The use according to claim 5, wherein the one or more semi-aromatic polyamides are selected from copolyamides made from a) group A monomers selected from terephthalic acid and hexamethylenediamine; and b) group B monomers selected from adipic acid and hexamethylenediamine.
 7. The use according to any preceding claim, wherein the resin composition further comprises one or more unfunctionalized polyolefins selected from polyethylenes, unfunctionalized polypropylenes, unfunctionalized ethylene alpha-olefin copolymers, unfunctionalized ethylene propylene diene rubbers (EPDM) and mixtures thereof.
 8. The use according to any preceding claim, wherein the resin composition further comprises one or more plasticizers selected from sulfonamides, esters of hydroxybenzoic acids, tetrahydrofurfuryl alcohol esters or ethers, esters of citric acid or of hydroxymalonic acid and mixtures thereof.
 9. The use according to any preceding claim, wherein the hollow structure further comprises an innermost layer made of a material other than the resin composition.
 10. The use according to any preceding claim, wherein the hollow structure further comprises an outermost layer made of a material other than the resin composition.
 11. The use according to any preceding claim, wherein the hollow structure further comprises one or more functional layers.
 12. The use according to any preceding claim, wherein the hollow structure is in the form of a hose, a pipe, a duct, a tube, tubing or a conduit.
 13. The use according to any preceding claim, wherein the refrigerant fluid comprises a hydrofluoroolefin (HFO).
 14. The use according to claim 13, wherein the hydrofluoroolefin is 2,3,3,3-tetrafluoropropene.
 15. A refrigerant device comprising the hollow structure as recited in anyone of claims 1 to
 12. 16. A method for conveying a refrigerant fluid comprising passing the refrigerant fluid through a hollow structure comprising a layer made of a resin composition comprising one or more semi-aromatic polyamides and one or more functionalized polyolefins, wherein the one or more semi-aromatic polyamides are selected from copolyamides made from: a) group A monomers selected from: i) aromatic dicarboxylic acids having 8 to 20 carbon atoms and aliphatic diamines having 4 to 20 carbon atoms; or ii) aliphatic dicarboxylic acids having 6 to 20 carbon atoms and aromatic diamine having 6 to 20 carbon atoms; or iii) aromatic aminocarboxylic acid having 7 to 20 carbon atoms and b) group B monomers selected from: iii) aliphatic dicarboxylic acids having 6 to 20 carbon atoms and aliphatic diamines having 4 to 20 carbon atoms; or iv) lactams and/or aliphatic aminocarboxylic acids having 4 to 20 carbon atoms, i) wherein the monomers of group A are present in an amount from at or about 10 mole-percent to at or about 40 mole-percent based on the copolyamide, and the monomers of group B are present in an amount from at or about 60 mole-percent to at or about 90 mole-percent based on the copolyamide.
 17. The method according to claim 16, wherein the one or more functionalized polyolefins are maleic anhydride grafted polyolefins.
 18. The method according to claim 16, wherein the one or more functionalized polyolefins are selected from maleic anhydride grafted polyethylenes, maleic anhydride grafted polypropylenes, maleic anhydride grafted ethylene alpha-olefin copolymers or maleic anhydride grafted ethylene-propylene diene rubber and mixtures thereof.
 19. The method according to claim 16, wherein the one or functionalized polyolefins are present in an amount from 10 to 30 weight percent, the weight percentages being based on the total weight of the resin composition.
 20. The method according to claim 16, wherein the one or more semi-aromatic polyamides are selected from copolyamides made from: a) group A monomers selected from terephthalic acid and hexamethylenediamine; terephthalic acid and tetramethylenediamine; and b) group B monomers selected from adipic acid and tetramethylenediamine; adipic acid and hexamethylenediamine; decanedioic acid and hexamethylenediamine; dodecanedioic acid and hexamethylenediamine; caprolactam; laurolactam; 11-aminoundecanoic acid; a) group A monomers selected terephthalic acid and decamethylenediamine; and b) group B monomers selected from decanedioic acid and decamethylenediamine; a) group A monomers selected adipic acid and m-xylylenediamine; and b) group B monomers selected from adipic acid and hexamethylenediamine; and mixtures thereof.
 21. The method according to claim 16, wherein the one or more semi-aromatic polyamides are selected from copolyamides made from a) group A monomers selected from terephthalic acid and hexamethylenediamine; and b) group B monomers selected from adipic acid and hexamethylenediamine.
 22. The method according to claim 16, wherein the resin composition further comprises one or more unfunctionalized polyolefins are selected from polyethylenes, unfunctionalized polypropylenes, unfunctionalized ethylene alpha-olefin copolymers, unfunctionalized ethylene propylene diene rubbers (EPDM) and mixtures thereof.
 23. The method according to claim 16, wherein the resin composition further comprises one or more ionomers.
 24. The method according to claim 16, wherein the composition resin further comprises one or more plasticizers selected from sulfonamides, esters of hydroxybenzoic acids, tetrahydrofurfuryl alcohol esters or ethers, esters of citric acid or of hydroxymalonic acid and mixtures thereof.
 25. The method according to claim 16, wherein the hollow structure further comprises an innermost layer made of a material other than the resin composition.
 26. The method according to claim 16, wherein the hollow structure further comprises an outermost layer made of a material other than the resin composition.
 27. The method according to claim 16, wherein the hollow structure further comprises one or more functional layers.
 28. The method according to claim 16, wherein the hollow structure is in the form of a hose, a pipe, a duct, a tube, tubing or a conduit.
 29. The method according to claim 16, wherein the refrigerant fluid comprises a hydrofluoroolefin (HFO).
 30. The method according to claim 16, wherein the refrigerant fluid comprises 2,3,3,3-tetrafluoropropene.
 31. A refrigerant device comprising the hollow structure recited in claim
 16. 